Hi,

I would like to ask a question or two down the line.

A rich running car usually happens when the computer is being told the engine is colder than it really is.
By changing the ECT you attempted to correct that but is that signal getting to the computers.
The circuit might be wide open and the engine is being treated as if it were in Alaska.
You may want to take a resistance reading of those pins on the ECU noted in the Bentley that also give voltages readings by back probing with the key on.
There may be some posts on this topic.

The next thing is a stuck open thermostat. If you are not running a Wahler thermostat this happens a lot from my experience. Also I like a 92 C degree one and the Wahler is more accurate over a long time interval. They are worth a couple dollars more and the hassle to get.

Have you ever taken the temperature compensation board out of the instrument cluster?
You may want to do that so the gauge cannot lie to you by upstaging the actual coder temperature to a higher one.

With a Wahler in there, the gauge will run with the needle horizontal and nail that position in shorter order for quicker warmups.
I have tested the operation of stats in vegetable oil and can see quite early on, the opening action of the valve plate or restriction. It opens slower and reacts slower going both ways to keep the engine on temperature. With oil I can push the thermostat to any temperature I want, up or down, for as long as I want.

IMHO the Calorstat brands are over pushed in parts stores and Stants are just as unreliable in performance and subject to customer damage being bubble carded.
I'm suspicious that they are "profit marketed" more that Borg Warners - Wahler stats.
I personally like that feature to make up for short runs to town. It helps to get heat into the engine oil to drive off moisture in the oil. Acids are formed using water. The less water the less acids.

Any way verify the engine temperature with a infrared thermometer on the engine block or outlet hose if possible.

Phil

Sulfur smell in exhaust suggest too much fuel is delivered into the engine. For sometime. Your catalytic converter may be failing. Perhaps clogged in part.

Art Benstein may suggest checking fuel pressure using the Schrader valve on the fuel rail.

https://www.brickboard.com/FAQ/700-900/EnginePerformanceSymptoms.htm

You can smell rich running condiction at first cold start and the exhaust smells over rich of unburnt fuel.

https://www.brickboard.com/FAQ/700-900/EngineFIComputer.htm

See other articles in the FAQ.

Other than socket 2 (fuel control) fault code 1-2-3 - ECT issue, any other codes? Socket 6 for ignition fault codes. The CHECK ENGINE light is on?

Have you checked for leaking injectors? From 23 MPG to 9 MPG is a rather serious drop. I guess the Odometer is clokcing up accuratley versus your hand-held GPS?

In the air filter box is the preheat flap valve. Thermostatically controlled by an amibent air inlet, a thermostat controls the flap valve. Always fails to hot and will wreck the AMM / MAF - though your replaced it. Preheat air is drawn through the silver accordion like air tube between the exhaust manifold and the lower air filter box inlet obscured from quick view by the fan cowl.

The exhaust is secured along all hanger attachment points. The biggy is the hanger at the header pipe upstream of the header pipe out to catalytic converter inlet. The three point securing hardware is weak at this union. You may not hear a leak, yet any leak may allow air to be drawn into the exhaust here and the oxygen snesor encounters extra oxygen, so the engine fuel control, your white label 561, reponds by adding more fuel.

As you reside in the toilet midwest as I do, I'm in nnearby Arches city with the stupid baseball cardinals and NHL hockey blues, slovenly humidity this region puts up (Mexico Gulf) and a single snow flake and tonnes of road salt enhance corrosion of all sorts. DeoxIT-D is your pal with low volt DC connections. (Won't deal with the rust, tho.)

I can't diagnose the cause, yet a drop to 9 MPG suggest a fuel delivery issue. Such as a leaking injector or over pressure at the fuel rail. You did install a new Bosch FPR? Yet no accounting for 'quality' anymore.

Though it is good to have known good spares, like the fuel and ignition computers. Another white 561 or the newer, more durable, -951 found in 940 normally aspired (no turbo), no EGR. -9xx Bosch injection boxes to not power nor have connection to the cold start injector valve.

I believe your 1992 model year deleted the cold start valve injector. Though with the LH-2.4, you will have cold start valve.

Also, an air intake leak downstream of the AMM / MAF, including the air intake port manifold gasket, causes a lean running condition.

And you have emissions checked in IL-state, yes?
--
Give your brickboard.com a big thumbs up! Way up! - Roger Ebert.

Update to the original post.

I've replaced;

CPS
FPR

Checked cap/rotor for defect

Yet continue with "not so hard" start but have noticed my fuel consumption has gone from about 23 mpg to 9 mpg!

Running very rich obviously, accompanied by sulfur smell from exhaust.

I'm thinking the white label 561 is bad.
Any thoughts?

I had the exact same symptoms recently. It turned out to be my rotor, which I had replaced no more than a year earlier. The end of it was black with carbon build up. I cleaned it up and no more problems.
--
Bruce S. near D.C.

Thanks for tips machine man. I will perform and report the results.

Hi, this is where I would look, if you haven't already?

You have eliminated the CPS failure symptoms.
Just curious, Have you checked the spark relay that resides behind the battery. That connection sometimes get a little corrosion going on.
It's recommend,by me, that it be removed every ten years or less and check its connector and grounding wire. While you're at it, take the heat sink plate off the back of the component and renew the whitish heat conduct paste. This helps during hot summers to keep it alive.


Have you tried turning the ignition switch to the second position and off again a few times to tun the fuel pumps.
This should pressurize the fuel line and the fuel rail up to a full volume before you actually try to start the engine.
Do this when are pretty sure that the engine is like it has treated you before and did long cranks.

If this process shortens the fail to start time any at all then if MAY prove that you have a leakage on the pressure side of the fuel system. A leaky FPR or one of four injectors is possible and will do tthis over time.

Since it runs smoother during warmups could mean all of the above or a leaky intake manifold gasket.